The present invention relates to an electric power steering system and a controller of the electric power steering system, which provides a steering assist force to a steering mechanism of a vehicle with an electric motor being a driving source.
In recent years, there have been proposed and developed various electric power steering systems. In the electric power steering systems, a rotation angle of an input shaft which rotates by driver's steering operation of a steering wheel and a rotation angle of an output shaft to which the rotation of the input shaft is transmitted are detected by a detector such as a torque sensor, and on the basis of this detection signal of the torque sensor, torque is transmitted to the steering mechanism of the vehicle from the electric motor. In this manner, the electric power steering system performs the steering assist.
In one such electric power steering system, a judgment is made as to whether a detection (or a detection value) of the torque sensor or a steering angle sensor is a normal input (or a forward input) according to driver's intention or a reverse input from an output shaft side caused by disturbance, by a rate of change of the detection signal of the torque sensor or the steering angle sensor. Then when judging that the detection is the reverse input by disturbance, a disturbance compensation torque is provided to the steering mechanism from the electric motor, thereby stabilizing vehicle behavior and improving steering feel (for instance, Japanese Patent Provisional Publication No. 2010-036720 (hereinafter is referred to as “JP2010-036720”)).